In recent years, attention has been drawn to global environmental problems such as those of exhaust gas, disruption of the ozone layer and the like, and it is urgently necessary to improve the energy efficiency of an internal combustion engine in an automobile or the like. One method of improving the energy efficiency that has been studied is lightening of the parts forming the internal combustion engine. Namely, replacement of parts that have generally been prepared from iron group metals with aluminum group parts has been studied.
However, aluminum group materials generally have an inferior sliding property, and hence it is necessary to partially prepare the aluminum group parts from ceramic which has a superior sliding property and which is further superior in wear resistance.
A number of materials are known as ceramics, as shown in Table 1. Silicon nitride is most promising as a material which has an excellent sliding property and comprises necessary characteristics such as strength and toughness as a machine part while maintaining the advantage of being lightweight as an aluminum group material. Therefore, methods of joining aluminum group materials with silicon nitride sintered bodies have been studied in various fields.
TABLE 1 ______________________________________ Specific Material Gravity Strength Toughness Slidability Cost ______________________________________ Si.sub.3 N.sub.4 O O O O O SiC O X X O O AlN O X X X O Al.sub.2 O.sub.3 X X X O O ZrO.sub.2 X O .circleincircle. X O mullite X X O X O B.sub.4 C .circleincircle. X X O X ______________________________________
For example, Japanese Patent Laying-Open No. 6-172052 discloses a method of engaging a ceramics part with an aluminum group material. According to such a mechanical joining method, a problem exists in that the joined members can be separated by an external applied load since the joining strength is generally small. Further, there has been a further problem in that a clearance is defined between the engaged portions as the temperature increases due to the difference between the thermal expansion coefficients (that of ceramics is smaller in most case) between the ceramics part and the aluminum group material. As the temperature further increases, the separation is further enlarged, while the ceramics part is displaced with respect to the aluminum group material and positional accuracy cannot be ensured.
In order to solve such problems, formation of chemical bonding between the ceramics and the aluminum group material has been studied. As the most general method of joining ceramics with a metal, there is a method of metallizing a surface of ceramics by the so-called Mo--Mn method and thereafter brazing the same with a brazing material of a noble metal, or a method of performing brazing using a so-called active metal brazing material which is prepared by adding an active metal such as titanium (Ti) to a noble metal brazing material for improving reactivity with ceramics while omitting metallization. Both of these methods cannot be applied to aluminum group materials having low melting points, since it is necessary to perform heating to high temperatures of at least 700.degree. C. On the other hand, joining by using a solder which is melted at a lower temperature is also conceivable. According to this method, however, it is difficult to remove a strong oxide film from a surface of an aluminum group material, and it has been impossible to join ceramics and an aluminum group material with each other.
Due to such a technical background, Japanese Patent Laying-Open No. 61-209965, for example, discloses a method of arranging a metal (Fe, Co, Ni, Pt or the like) having high reactivity on a surface of a silicon nitride sintered body, metallizing the same preferably in a vacuum atmosphere of at least 1200.degree. C., thereafter bringing the same into contact with aluminum or its alloy, and heating and joining the same at a temperature below its eutectic temperature. However, this method disadvantageously leads to increase of the preparation cost since this metallization step includes troublesome treatments such as application of the metal and a high temperature treatment in a vacuum.
As a method of improving wear resistance of a metal surface, ceramic coating by CVD or PVD is conceivable. According to such a method, however, there have been such problems that the coating layer is separated, and that the rigidity of the coating surface is insufficient when a base material is prepared from an aluminum group material.
As hereinabove described, it has been difficult in the prior art to join a member consisting of silicon nitride to a base material or a backing which is mainly composed of aluminum.